Study of the contamination rate and change in growth features of lettuce (Lactuca sativa Linn.) in response to cadmium and a survey of its phytochelatin synthase gene

Combined application of zinc oxide and iron nanoparticles enhanced Red Sails lettuce growth and antioxidants enzymes activities while reducing the chromium uptake by plants grown in a Cr-contaminated soil

Soil contamination with chromium (Cr) is becoming a primary ecological and health concern, specifically in the Kasur and Sialkot regions of Pakistan. The main objective of the current study was to evaluate the impact of foliar application of zinc oxide nanoparticles (ZnO NPs) (0, 25, 50, 100 mg L-1) and Fe NPs (0, 5, 10, 20 mg L-1) in red sails lettuce plants grown in Cr-contaminated soil. Our results showed that both ZnO and Fe NPs improved plant growth, and photosynthetic attributes by minimizing oxidative stress in lettuce plants through the stimulation of antioxidant enzyme activities. At ZnO NPs (100 mgL-1), dry weights of shoots and roots and fresh weights of shoots and roots were improved by 53%, 58%, 34%, and 45%, respectively, as compared to the respective control plants. The Fe NPs treatment (20 mgL-1) increased the dry weight of shoots and the roots and fresh weights of shoots and roots by 53%, 76%, 42%, and 70%, respectively. Application of both NPs reduced the oxidative stress caused by Cr, as evident by the findings of the current study, i.e., at the ZnO NPs (100 mgL-1) and Fe NPs (20 mgL-1), the EL declined by 32% and 44%, respectively, in comparison with respective control plants. Moreover, Fe and ZnO NPs enhanced the Fe and Zn contents in red sails lettuce plants. Application of ZnO NPs at 100 mg L-1 and Fe NPs at 20 mg L-1, improved the Zn and Fe contents in plant leaves by 86%, and 68%, respectively, as compared to the control plants. This showed that the exogenous application of these NPs helped in Zn and Fe fortification in plants. At similar of concenteration ZnO NPs, CAT and APX activities were improved by 52% and 53%, respectively. Similarly, the POD contents were improved by 17% and 45% at 5 and 10 mg/L of Fe NPs. Furthermore, ZnO and Fe NPs limited the Cr uptake by plants, and the concentration of Cr in the leaves of lettuce was under the threshold limit. The exogenous application of ZnO NPs (100 mg L-1) and Fe NPs (20 mg L-1) reduced the Cr uptake in the leaves of red sails lettuce by 57% and 51%, respectively. In conclusion, ZnO and Fe NPs could be used for the improvement of plant growth and biomass as well as nutrient fortification in stressed environments. These findings not only underscore the efficacy of nanoparticle-assisted phytoremediation but also highlight its broader implications for sustainable agriculture and environmental health. However, future studies on other crops with molecular-level investigations are recommended for the validation of the results.

Phytochelatin-Mediated Cultivar-Dependent Cd Accumulations of Lactuca sativa and Implication for Cd Pollution-Safe Cultivars Screening

Cd pollution-safe cultivar (Cd-PSC) is a feasible strategy to minimize Cd contamination in leafy vegetables. The shoot Cd concentrations of 23 Lactuca sativa cultivars under Cd stress ranged from 0.124 to 2.155 mg·kg-1 with a maximum cultivar difference of 8 folds. Typical Cd-PSC C16 (L) and high-Cd-accumulating cultivar C13 (H) were screened to investigate the mechanisms of Cd accumulations in L. sativa through determining Cd concentrations, Cd subcellular distributions, phytochelatin profiles, and phytochelatin biosynthesis-related genes' expressions. Higher Cd distribution in a heat stable fraction in C13 (H) indicated that the high Cd accumulation trait of C13 (H) mainly depended on the Cd-phytochelatin complexes. Root phytochelatin concentrations were significantly elevated in C13 (H) (5.83 folds) than in C16 (L) (2.69 folds) (p < 0.05) under Cd stress. Significantly downregulated expressions of glutathione S-transferase rather than the regulation of phytochelatin synthesis genes in the root of C13 (H) might be responsible for sufficient glutathione supply for phytochelatins synthesis. These findings suggested that phytochelatin elevation in C13 (H) would favor the Cd root to shoot transportation, which provides new insights into the phytochelatin-related cultivar-dependent Cd accumulating characteristic in L. sativa.

Combined interactions of amino acids and organic acids in heavy metal binding in plants

This research focused on the different approaches to the transport and internal chelation of metals with amino acids and organic acids in plants. Therefore, in the first phase, the plants studied were identified the characteristics of the bioaccumulation factors. Steria pumila, Echium angustifolium, Typha angustifolia, Sisymbrium austriacum were identified as hyperaccumulators (Cd, Ni), accumulators (Pb, Sn, and Se), excluders (Cr, Hg). On the other hand, the Sisymbrium austriacum only showed the characteristic of the accumulator for Cr. In the second phase, the combined effects of amino acids and organic acids on the chelation of heavy metals in plants were tested by a multi-linear regression model. Related to our hypothesis, Amino acids; Gly and Leu (Cd), Trp and Ile (Pb), Asp, Ser, and Leu (Cr), Ser (Hg), Trp and Glu (Ni), Asp, Thr, and Gly (Sn), Asn and Leu (Se), Organic acids; Malonic and Malic acid (Cd), Malonic acid (Pb), Oxalic and Malic acid (Cr), Oxalic, Succinic, Citric and Butyric acid (Hg), Malonic and Malic acid (Ni), Malonic, Maleic, and Malic acid (Sn), Malonic and Citric acid (Se) were concluded that had combined effect for heavy metal's phytochelation ability into plants.

Correlation of Elemental Transfer, Bioactive Compounds and Antioxidant Activity on Lactuca sativa L. Grown in Soil with Functionalized CNT and HMs

While heavy metals (HM) have been considered in recent decades to be the most common and problematic pollutants, the expansion of the list of pollutants due to the active use of carbon nanotubes (CNT) raises new questions about the benefit and harm of HM released to nature individually or fixed on CNT walls. A pot experiment was conducted to compare the effect of two classes of potential pollutants-metal salts of Pb, Mn, Cu, Zn, Cd, and Ni; and functionalized CNTs with COOH, MnO2, Fe3O4, and MnO2-Fe3O4-applied in soil, on the elemental transfer, the bioactive compounds accumulation, and the antioxidant activity in lettuce. While CNTs mainly increased the elemental transfer from soil to leaves, HM salts strongly obstructed it. In the presence of CNTs, the antioxidant activity in lettuce leaves correlated with the transfer of elements from soil to root and from root to leaves. The excess of HMs in soil induced a greater variation of the polyphenols quantity and antioxidant activity than the excess of CNTs. It might be assumed that lettuce perceived HMs as a more aggressive stressor than CNTs and more strongly activated the defense mechanism, showing the reduction of the element transfer and enhancing of total polyphenol production and antioxidant activity.

Arbuscular mycorrhizal fungi and nitric oxide alleviate cadmium phytotoxicity by improving internal detoxification mechanisms of corn plants

Plants develop several external and internal mechanisms to increase their tolerance to heavy metals (HMs) toxicity including cadmium (Cd). Symbiosis with arbuscular mycorrhizae fungi (AMF) is one of the plants' strategies to tolerate HMs toxicity. Nitric oxide (NO), as a signaling molecule, is also involved in physiological responses of plants to various stresses. The present work was conducted as a factorial completely randomized design with three replications to study the effects of Funneliformis mosseae fungi and Sodium nitroprusside (SNP, 100 mM) as a donor of NO alone, in combination (AMF + SNP) on corn plant growth, and internal detoxification mechanisms of Cd toxicity in a Cd-contaminated calcareous soil (0, 25, 50, and 100 mg Cd kg-1). The results showed that under Cd stress, AMF inoculation and/or foliar application of SNP significantly increased plant growth (32% to 103% for shoot and 44% to 84% for root) by decreasing Cd concentration in corn plant tissues (23% to 46% for shoot and 19% to 40% for root). Cd-induced oxidative stress was mitigated by AMF and/or SNP by enhancing the activities of antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT), and concentration of non-enzymatic antioxidants such as glutathione (GSH) and phytochelatin (PC). Increasing the tolerance index (TI) and decreasing the transfer factor (TF) in the corn plants treated with AMF and/or SNP, confirm the efficient role of SNP and AMF in stimulating the detoxification mechanisms of Cd within the plant cells, which was more pronounced at the lowest Cd level (25 mg Cd kg-1). In conclusion, symbiotic associations of corn plants with AMF alone or in combination with SNP mitigated the detrimental effect of Cd toxicity in corn grown in Cd-contaminated calcareous soil. The corn's internal detoxification mechanisms lowered the Cd concentration in plant tissue which resulted in the improvement of the corn's growth parameters.

Phytoremediation as an Effective Remedy for Removing Trace Elements from Ecosystems

The pollution of soil by trace elements is a global problem. Conventional methods of soil remediation are often inapplicable, so it is necessary to search intensively for innovative and environment-friendly techniques for cleaning up ecosystems, such as phytoremediation. Basic research methods, their strengths and weaknesses, and the effects of microorganisms on metallophytes and plant endophytes resistant to trace elements (TEs) were summarised and described in this manuscript. Prospectively, bio-combined phytoremediation with microorganisms appears to be an ideal, economically viable and environmentally sound solution. The novelty of the work is the description of the potential of "green roofs" to contribute to the capture and accumulation of many metal-bearing and suspended dust and other toxic compounds resulting from anthropopressure. Attention was drawn to the great potential of using phytoremediation on less contaminated soils located along traffic routes and urban parks and green spaces. It also focused on the supportive treatments for phytoremediation using genetic engineering, sorbents, phytohormones, microbiota, microalgae or nanoparticles and highlighted the important role of energy crops in phytoremediation. Perceptions of phytoremediation on different continents are also presented, and new international perspectives are presented. Further development of phytoremediation requires much more funding and increased interdisciplinary research in this direction.

Metal tolerance mechanisms in plants and microbe-mediated bioremediation

The heavy metal contamination, which causes toxic effects on plants, has evolved into a significant constraint to plant quality and yield. This scenario has been exacerbated by booming population expansion and intrinsic food insecurity. Numerous studies have found that counteracting heavy metal tolerance and accumulation necessitates complex mechanisms at the biochemical, molecular, tissue, cellular and whole plant levels, which may demonstrate increased crop yields. Essential and non-essential elements have similar harmful impacts on plants including reduced biomass production, growth and photosynthesis inhibition, chlorosis, altered fluid balance and nutrient absorption, as well as senescence, all of which led to plant death. Notable biotechnological strategies for effective remediation require knowledge of metal stress and tolerance mechanisms in plants. Assimilation, cooperation and integration, of biotechnological improvements, are required for adequate environmental rehabilitation in the emerging area of bioremediation. This review emphasizes a deeper understanding of metal toxicity, stress, and potential tolerance mechanisms in plants exposed to metal stress. The microbe-mediated metal toxic effects and stress mitigation knowledge can be used to create a new strategic plan as feasible, sustainable, and environmentally friendly bioremediation techniques.

Microbial community assembly of the hyperaccumulator plant Sedum plumbizincicola in two contrasting soil types with three levels of cadmium contamination

Microbial communities are closely related to plant performance and numerous studies have shown their involvement with the growth and development of host plants, resistance to pathogen invasion and adaptation to environmental stress. Here we described in detail the ecological process of the microbial community assembly in hyperaccumulator plant Sedum plumbizincicola. We divided the microbiota into four ecological compartments (bulk soil, rhizosphere, root endosphere and aboveground endosphere). The results showed that host selection strongly controlled the aggregation of microbial community. So that microbes occupied different niches from the bulk soil to the aboveground endosphere, and bacterial diversity and network complexity decreased gradually. Soil types were the second influencing factor, especially for the microbial community in the root endosphere. The SourceTracker analysis further confirmed the vertical migration of microbes from bulk soil to aboveground endosphere. In addition, under the condition of heavy metal pollution, the microbial community of S. plumbizincicola tended to form a microbial pool dominated by Proteobacteria and Actinobacteria. Ellin6067, Sphingomonas, Ralstonia, SC-I-84_uncultured bacterium, Burkholderiaceae_Undibacterium and Pedosphaeraceae_uncultured bacterium etc. were identified as the vital biomarker taxa. Among these genera, the relative abundance of last three was significantly positively correlated with the activation and transfer of cadmium, and they mainly enriched in paddy soil. This study provides evidence for the mechanism by which the microbial community assembly occurs and experience for regulating the microbial community and increasing the accumulation efficiency of potentially toxic metals in S. plumbizincicola.

Investigation of the combined effects of cadmium chloride, silver nitrate, lead nitrate, methyl jasmonate, and salicylic acid on morphometric and biochemical characteristics of St. John's wort

Hypericum perforatum L., is a sprawling, leafy herb that grows in open, disturbed areas, known as St. John's wort, has a variety of secondary metabolites that can be used for medicinal and therapeutic purposes. Heavy metals have become the most dangerous pollutants in the environment. The effect of cadmium chloride, lead nitrate, silver nitrate, methyl jasmonate, and salicylic acid was studied on several morphometric and biochemical features of St. John's wort simultaneously using the Taguchi statistical method. The results showed cadmium chloride and lead nitrate reduced the morphometric and biochemical properties of St. John's wort while salicylic acid compensated for the adverse effects of heavy metals. Simultaneously, use of salicylic acid and silver nitrate with cadmium chloride and lead nitrate reduced the toxic effects of these metals on morphometric properties. Methyl jasmonate improved growth characteristics at low levels and inhibited at higher levels. Also, according to the results, salicylic acid could reduce the effects of heavy metals on the biochemical properties, while silver nitrate acts like heavy metals, especially at higher levels. Salicylic acid reduced the harmful effects of these heavy metals and at all levels was able to create a better induction effect on St. John's wort. These elicitors mainly changed the adverse effects of heavy metals by strengthening the pathways of the antioxidant system in St. John's wort. The research assumptions were validated, which suggests that the Taguchi method could be considered in an optimum culture of medicinal plants under different treatments such as heavy metals and elicitors.

Phytochelatins: Sulfur-Containing Metal(loid)-Chelating Ligands in Plants

Phytochelatins (PCs) are small cysteine-rich peptides capable of binding metal(loid)s via SH-groups. Although the biosynthesis of PCs can be induced in vivo by various metal(loid)s, PCs are mainly involved in the detoxification of cadmium and arsenic (III), as well as mercury, zinc, lead, and copper ions, which have high affinities for S-containing ligands. The present review provides a comprehensive account of the recent data on PC biosynthesis, structure, and role in metal(loid) transport and sequestration in the vacuoles of plant cells. A comparative analysis of PC accumulation in hyperaccumulator plants, which accumulate metal(loid)s in their shoots, and in the excluders, which accumulate metal(loid)s in their roots, investigates the question of whether the endogenous PC concentration determines a plant's tolerance to metal(loid)s. Summarizing the available data, it can be concluded that PCs are not involved in metal(loid) hyperaccumulation machinery, though they play a key role in metal(loid) homeostasis. Unraveling the physiological role of metal(loid)-binding ligands is a fundamental problem of modern molecular biology, plant physiology, ionomics, and toxicology, and is important for the development of technologies used in phytoremediation, biofortification, and phytomining.

Risk Assessment of Heavy Metal in Farmlands and Crops Near Pb-Zn Mine Tailing Ponds in Niujiaotang, China

To accurately evaluate the pollution and risk of heavy metals in crops and farmlands near mines, we determined the contents of Cr, Ni, Cu, As, Cd, Pb, and Zn in 10 farmland soil sampling sites and six crops (pak choi, rice, spring onion, radish, Chinese cabbage, Chrysanthemum coronarium) in an area near the Niujiaotang Pb-Zn mine in Duyun City, China. Four evaluation methods were compared, including the potential ecological hazard index, Nemeiro comprehensive pollution assessment, risk assessment code, and the ratio of secondary phase to primary phase methods. The average concentration of As, Cd, Pb, and Zn exceeded the soil environmental background levels in Niujiaotang and Guizhou Province. Cd exceeded the standard substantially, and Zn pollution accumulation was the most evident. Heavy metal contamination of crops was in the order pak choi > Chinese cabbage > spring onion > paddy > radish > Chrysanthemum coronarium, whereas heavy metal concentration in crops were in the order Zn > As > Cr > Cd > Ni > Pb. The levels of all heavy metals except Cu exceeded Chinese food hygiene standards. Carcinogenic and non-carcinogenic chemicals in crops present significant risks to adults and children. Risk evaluation considering the morphological contents of heavy metals rather than their total concentration was more accurate for environmental quality assessment of agricultural soils. Samples should be collected at different times to study the spatial and temporal distribution, and further studies on the migration transformation of heavy metals between the tailings pond-soil-crop should be conducted.

Intercropping affects the physiology and cadmium absorption of pakchoi, lettuce, and radish seedlings

Intercropping can affect the growth and elemental absorption of vegetables. This study investigated the physiology and cadmium (Cd) content of pakchoi (Brassica chinensis L.), lettuce (Lactuca sativa L. var. ramosa Hort.), and radish (Raphanus sativus L.) seedlings under monoculture, mutual intercropping of two or three varieties. Intercropping is not conducive to the accumulation of chlorophyll and biomass content of pakchoi, lettuce, and radish. When three seedlings were intercropped together, the antioxidant enzyme activity of pakchoi, lettuce, and radish increased and the content of malondialdehyde decreased, except that the superoxide dismutase activity of radish is inferior to the value of radish and pakchoi intercropping. Intercropping increased the soluble sugar and proline content in the lettuce seedlings, while those in the radish and lettuce seedlings reduced or had no significant effect. When intercropped with pakchoi and lettuce, the Cd content in the roots and shoots of pakchoi is higher and lower, respectively. At the same time, root or shoot bio-concentration factors also performed the same trend, and TF was the smallest and less than 1; however, the TF of lettuce is greater than 1. When intercropping with pakchoi or lettuce separately or together, it promoted the accumulation of Cd in radish root; when intercropping with pakchoi, the value of TF was the smallest. From the antioxidant system, the performance of the three seedlings intercropped together is better than the two; however, the accumulation of Cd shows the opposite trend, and the participation of cabbage in the intercropping is relatively conducive to reducing the Cd content in the edible parts.

Combined cadmium and fluorine inhibit lettuce growth through reducing root elongation, photosynthesis, and nutrient absorption

Cadmium (Cd) and fluorine (F) often coexist in environment and are toxic to organisms; however, their combined effects on plants are still not well documented. In this study, the co-effects of Cd and F on germination, biomass, photosynthesis, and nutrients uptake of lettuce were carried out in hydroponic culture. The results showed that the seed germination and seedling biomass decreased with an increase in Cd and F supplementation. The root morphology verified these effects as excess combined Cd and F diminished the root tips and surface area of lettuce, while single Cd and F inhibited the growth by decreasing root length and average diameter, respectively. These effects were also consistence with a reduction in photosynthesis which was mainly regulated by reducing the quantum yield of PS II, electron transport activity, stomatal conductance, intercellular CO2 concentration, and transpiration rate in response to the pollutants. Moreover, when lettuce exposed to Cd and F stress, the accumulation of several essential elements in shoot decreased. In a sum, the synergistic negative effects of Cd and F on the seed germination and seedling growth of lettuce were observed, and these might be owed to nutrient absorption and translocation in the plant. These findings aid in understanding the harmful effects and specific mechanisms of action of Cd and F on plants.

Construction and carbon source optimization of a microbial-plant coupled reactor for treating acid mine drainage

Acid mine drainage (AMD) is recognized as one of the most serious contamination sources in the nonferrous metal mining industry. In this study, aerobic strains VCZ02 and VCZ09, which were identified as Leclercia adecarboxylata and Klebsiella aerogenes, were screened from 11 strains of copper-zinc-resistant bacteria in the soil of the Dexing copper mine with Cu²⁺/Zn²⁺ removal rates of 46.32%/41.03% and 57.96%/67.05%, respectively. The composition of extracellular polymers plays an important role in the removal of heavy metals by these two strains. A mixed community consisting of VCZ02 and VCZ09 was coupled with Sagittaria trifolia L.var.sinensis (Sims) Mak to construct a microbial-plant coupled reactor to remediate AMD. Under the optimal condition of sodium acetate as carbon source, the pH of AMD increased from less than 5 to above 6.5, showing Cu²⁺/Zn²⁺ removal rates of 70-80% and above 30%, respectively. SEM-EDS results showed that VZC02 and VZC09 in the coupled reactor also helped with resisting the toxicity of heavy metals to plants by forming biofilms on the root surface and increasing the content of heavy metals on the surface of roots, thus improving the treatment effect of plants. This study provides a theoretical basis for the bioremediation of AMD and its application.

Genome sequencing of biocontrol strain Bacillus amyloliquefaciens Bam1 and further analysis of its heavy metal resistance mechanism

Plant growth-promoting rhizobacteria (PGPR) or Biocontrol strains inevitably encounter heavy metal excess stress during the product's processing and application. Bacillus amyloliquefaciens Bam1 was a potential biocontrol strain with strong heavy metal resistant ability. To understand its heavy metal resistance mechanism, the complete genome of Bam1 had been sequenced, and the comparative genomic analysis of Bam1 and FZB42, an industrialized PGPR and biocontrol strain with relatively lower heavy metal tolerance, was conducted. The comparative genomic analysis of Bam1 and the other nine B. amyloliquefaciens strains as well as one Bacillus velezensis (genetically and physiologically very close to B. amyloliquefaciens) was also performed. Our results showed that the complete genome size of Bam1 was 3.95 Mb, 4219 coding sequences were predicted, and it possessed the highest number of unique genes among the eleven analyzed strains. Nine genes related to heavy metal resistance were detected within the twelve DNA islands of Bam1, while only two of them were detected within the seventeen DNA islands of FZB42. When compared with B. amyloliquefaciens type strain DSM7, Bam1 lacked contig L, whereas FZB42 lacked contig D and I, as well as just possessed contig B with a very small size. Our results could also deduce that Bam1 promoted its essential heavy metal resistance mainly by decreasing the import and increasing the export of heavy metals with the corresponding homeostasis systems, which are regulated by different metalloregulators. While Bam1 promoted its non-essential heavy metal resistance mainly by the activation of some specific or non-specific exporters responding to different heavy metals. The variation of the genes related to heavy metal resistance and the other differences of the genomes, including the different number and arrangement of contigs, as well as the number of the heavy metal resistant genes in Prophages and Genomic islands, led to the significant different resistance of Bam1 and FZB42 to heavy metals.

Antimony speciation, phytochelatin stimulation and toxicity in plants

Antimony (Sb) is a toxic metalloid that has been listed as a priority pollutant. The environmental impacts of Sb have recently attracted attention, but its phytotoxicity and biological transformation remain poorly understood. In this study, Sb speciation and transformation in plant roots was quantified by Sb K-edge X-ray absorption spectroscopy. In addition, the phytotoxicity of antimonate (Sb^V) on six plant species was assessed by measuring plant photosynthesis, growth, and phytochelatin production induced by Sb^V. Linear combination fitting of the Sb K-edge X-ray absorption near-edge structure (XANES) spectra indicated reduction of Sb^V was limited to ∼5-33% of Sb. The data confirmed that Sb-polygalacturonic acid was the predominant chemical form in all plant species (up to 95%), indicating Sb was primarily bound to the cell walls of plant roots. Shell fitting of Sb K-edge X-ray absorption fine-structure (EXAFS) spectra confirmed Sb-O and Sb-C were the dominant scattering paths. The fitting indicated that Sb^V was bound to hydroxyl functional groups of cell walls, via development of a local coordination environment analogous to Sb-polygalacturonic acid. This is the first study to demonstrate the key role of plant cell walls in Sb metabolism.

Foliar application of flavonoids (rutin) regulates phytoremediation efficiency of Amaranthus hypochondriacus L. by altering the permeability of cell membranes and immobilizing excess Cd in the cell wall

The gap between the current serious soil heavy metal (HM) contamination and the low efficiency of soil remediation threatens human health. The aim of this study was to propose a method to improve the efficiency of phytoremediation by exogenous rutin application and explain the potential mechanism. A series of rutin treatments were designed to evaluate the biomass, cadmium (Cd) accumulation and physiological and biochemical responses of Amaranthus hypochondriacus under different Cd stresses. The results showed a decline in cell membrane damage with rutin application, and more Cd ions were immobilized in the cell wall than in the vacuole, resulting in an increase in Cd tolerance in plants. The addition of rutin caused significant effects on the synthesis of glutathione (GSH), including the advancement of the conversion of GSH to phytochelatins (PCs). Among them, PC₂ and PC₃ in the leaves contributed the most to the high accumulation of Cd. Overall, the phytoremediation efficiency and phytoextraction amount of Amaranthus hypochondriacus with rutin application were improved maximumly by 219.48% and 260.00%, respectively. This study provides a constructive approach for improving the efficiency of phytoremediation by foliar application of flavonoids and contributes to the further development of soil remediation in Cd-contaminated fields.

Analyzing cadmium-phytochelatin2 complexes in plant using terahertz and circular dichroism information

Phytochelatins are plants' small metal-binding peptides which chelate internal heavy metals to form nontoxic complexes. Detecting the complexes in plants would simplify identification of cultivars with both high tolerance and enrichment capabilities for heavy metals which represent phytoextraction performance. Thus, a terahertz spectroscopy combined with density functional theory, chemometrics and circular dichroism was used for characterization of phytochelatin2 (PC₂), Cd-PC₂ mixture standards, and pak choi (Brassica chinensis) leaves as a plant model. Results showed PC₂ chelates Cd²⁺ in a 2:1 ratio to form Cd(PC₂)₂ complex; Cd connected to thoils of PC₂ and changed β-turn and random coil of PC₂ peptide chain to β-Sheet which presented as terahertz vibrations of PC₂ around 1.03 and 1.71 THz being suppressed; the best models for detecting the complex in pak choi were obtained by partial least squares regression modeling combined with successive projections algorithm selection; the models used PC₂ as a natural probe for visualizing and quantifying chelated Cd in pak choi leaf and achieved a limit of detection up to 1.151 ppm. This study suggested that terahertz information of the heavy metal-PCs complexes is qualified for representing a simpler alternative to classical index for evaluating phytoextraction performance of plant; it provided a general protocol for structure analysis and detection of heavy metal-PCs complexes in plant by terahertz absorbance.

Antibiotic Resistance Gene Transformation and Ultrastructural Alterations of Lettuce (Lactuca sativa L.) Resulting from Sulfadiazine Accumulation in Culture Solution

The research herein explored the possible mechanism of toxicity of the antibiotic sulfadiazine (SD) and the related antibiotic resistance gene transformation in lettuce by systematically investigating its growth responses, ultrastructural changes, and antibiotic resistance gene transformation via solution culture experiments. The results showed that SD mainly accumulated in the roots of lettuce at concentrations ranging from 6.48 to 120.87 μg/kg, which were significantly higher than those in leaves (3.90 to 16.74 μg/kg). Lower concentrations of SD (0.5 and 2.0 mg/L) in the culture nutrient solution exerted little effect on lettuce growth, while at SD concentrations higher than 10 mg/L, the growth of lettuce was significantly inhibited, manifesting as shorter root length and lower dry matter yield of whole lettuce plants. Compared with that for the control group, the absolute abundance of bacteria in the root endophyte, rhizosphere, and phyllosphere communities under different concentrations of SD treatment decreased significantly. sul1 and sul2 mainly accumulated in the root endophyte community, at levels significantly higher than those in the leaf endophyte community. Studies of electrolyte leakage and ultrastructural characteristics of root and leaf cells indicated that lettuce grown in culture solutions with high SD concentrations suffered severe damage and disintegration of the cell walls of organs, especially chloroplasts, in leaves. Furthermore, the possible mechanism of SD toxicity in lettuce was confirmed to start with the roots, followed by a free flow of SD into the leaves to destroy the chloroplasts in the leaf cells, which ultimately reduced photosynthesis and decreased plant growth. Studies have shown that antibiotic residues have negative effects on the growth of lettuce and highlight a potential risk of the development and spread of antibiotic resistance in vegetable endophyte systems.

Cadmium accumulation and physiological response of Amaranthus tricolor L. under soil and atmospheric stresses

In this study, cadmium (Cd) solution spraying and Cd-contaminated soil pot experiments were conducted to investigate the influence of Cd from atmospheric deposition and soil on the growth, cumulative distribution, chemical morphology, physiological, and biochemical responses of Amaranthus tricolor L. The results indicated that Cd in plants mainly came from soil (92-98%) and was stored in the roots in large quantities while the portion from atmospheric deposition could also effectively increase Cd content in stems and leaves (2-3%). Cd was mainly stored in plant cell walls and would transfer to the soluble part under high-concentration soil stress Cd from atmospheric deposition alone promoted the growth of plants, but high Cd concentrations from soil had the negative influence. The contents of H₂O₂ and MDA in plants increased under soil and atmospheric Cd stress, indicating that the plant cells were damaged by oxidative stress. The content of antioxidant enzymes such as POD, CAT, SOD, and antioxidants like AsA and GSH increased under low-concentration Cd stress but decreased under elevated stress, suggesting that high Cd-contaminated soil poses severe toxicity on the antioxidant system of the plants. Hence, the accumulation and physiological response of plants under multi-source Cd contamination were mainly affected by high soil Cd concentrations. Though the effect of atmospheric deposition is relatively less, it cannot be ignored.

Overexpression of BnPCS1, a Novel Phytochelatin Synthase Gene From Ramie (Boehmeria nivea), Enhanced Cd Tolerance, Accumulation, and Translocation in Arabidopsis thaliana

Phytochelatins (PCs) play important roles in the detoxification of and tolerance to heavy metals in plants. The synthesis of PCs is catalyzed by phytochelatin synthase (PCS), which is activated by heavy metal ions. In this study, we isolated a PCS gene, BnPCS1, from the bast fiber crop ramie (Boehmeria nivea) using the RACE (rapid amplification of cDNA ends) method. The full-length BnPCS1 cDNA is 1,949 bp in length with a 1,518 bp open reading frame (ORF) that encodes a 505 amino acid protein. The deduced BnPCS1 protein has a conserved N-terminus containing the catalytic triad Cys⁵⁸, His¹⁶⁴, Asp¹⁸², and a flexible C-terminal region containing a C³⁷¹C³⁷²QETC³⁷⁶VKC³⁷⁹ motif. The BnPCS1 promoter region contains several cis-acting elements involved in phytohormone or abiotic stress responses. Subcellular localization analysis indicates that the BnPCS1-GFP protein localizes to the nucleus and the cytoplasm. Real-time PCR assays show that the expression of BnPCS1 is significantly induced by cadmium (Cd) and the plant hormone abscisic acid (ABA). Overexpression lines of BnPCS1 exhibited better root growth and fresh weight, lower level of MDA and H₂O₂, and higher Cd accumulation and translocation factor compared to the WT under Cd stress. Taken together, these results could provide new gene resources for phytoremediation of Cd-contaminated soils.

Copper and zinc differentially affect root glutathione accumulation and phytochelatin synthase gene expression of Rhizophora mucronata seedlings: Implications for mechanisms underlying trace metal tolerance

Mangroves are susceptible to contamination due to their proximity to shores and human activities. Exposure to excessive trace metals can disturb their physiological functions and may eventually lead to death. Rhizophora mucronata is a common species growing in the mangrove forests of Thailand. Previous studies have shown that seedlings of R. mucronata are tolerant of trace metal and that they accumulate a large metal content in their root tissue. However, knowledge of their tolerance mechanisms is still lacking. To elicit the role of metal detoxification and sequestration by phytochelatins (PC) in the roots of R. mucronata seedlings, the impacts of Cu and Zn exposure were assessed on 1) physiological characteristics 2) the concentration of glutathione (GSH), a precursor of PC and 3) the level of the transcripts encoding phytochelatin synthase (PCS), the key enzyme for PC biosynthesis. Seedlings of R. mucronata were exposed to Cu and Zn in a hydroponic experiment (200 mg Cu or Zn/L in 1/4× Hoagland solution containing 8‰ NaCl, single addition). We found that both trace metals were largely accumulated in the roots. Only Cu-treated seedlings showed a decrease in the photosynthetic efficiency, in line with observed toxicity symptoms (i.e. bent stems and slight wilting of leaves). Metal accumulation, however, did not induce oxidative stress in the roots as indicated by similar level of total reactive species and lipid peroxidation across treatments. The GSH content in the roots exposed to Cu was significantly reduced while no change was observed in Zn-exposed roots. Coordinated semi-quantitative PCR and RT-qPCR revealed pcs down-regulation in Cu-treated roots, whereas Zn-treated roots showed a down-regulation on day 1 and a subsequent recovery on day 5. Failure of detoxification and sequestration of excess Cu due to GSH limitation and down-regulation of pcs may lead to the phytotoxic effects observed in Cu-treated plants. Our results suggest that both GSH and PC play an important role in trace metal tolerance in R. mucronata seedlings.

Response of Corchorus olitorius Leafy Vegetable to Cadmium in the Soil

Corchorus olitorius, a leafy vegetable with high nutrient content, is normally collected from the wild, in areas that are prone to cadmium (Cd) toxicity. However, studies on how Cd accumulation affects vegetative and reproductive traits of leafy vegetables in South Africa are limited. Therefore, this study tested the effect of Cd accumulation on C. olitorius morphological traits. Plants were grown under various Cd concentrations and studied for variation in vegetative and reproductive traits as well as accumulation in roots and shoots. Plants exposed to 5 mg/kg Cd had longer roots with higher moisture content, heavier fresh and dried stems, as well as dried leaves, which indicated a hormetic effect in C. olitorius after exposure to low Cd concentration in the soil. Again, plants treated with 5–10 mg/kg Cd, accumulated toxic (>10 mg/kg dry weight) Cd within shoots and roots, with minor morphological alterations. Plants could survive, with some morphological defects, Cd toxicity up to 20 mg/kg in soil. Only plants exposed to 5 mg/kg could reproduce. Cd accumulation increased with an increase in the soil, with higher accumulation in shoots. The translocation factor was high (>1) in all Cd concentrations. In conclusion, C. olitorius can accumulate toxic Cd, and yet grow and reproduce either normally or better than the control. The proposed dose of Cd that induces hormesis in C. olitorius is 5 mg/kg in the soil. Therefore, C. olitorius is suitable for phytoremediation of Cd contaminated soils, but unsafe for consumption when it grows in such areas.

Distribution of phytochelatins, metal-binding compounds, in plant foods: A survey of commonly consumed fruits, vegetables, grains and legumes

Phytochelatins (PyCs) are metal-binding compounds produced by plants. PyCs may reduce bioavailability of dietary toxic metals such as cadmium. However, the PyC concentrations in foods are unknown. The objective of this study was to analyze PyC contents in a subset of commonly consumed plant foods. Foods (20) across five groups were analyzed and PyCs quantified using liquid chromatography-mass spectrometry (LC-MS/MS). The impact of factors such as food processing were also explored. PyCs were in all 20 foods. Five PyC types were detected with PyC₂-Gly, PyC₃-Gly and PyC₂-Ala at quantifiable concentrations. PyC₂-Gly was found at the highest concentrations and most widely distributed. PyC₂-Gly concentrations were highest in fruits and root vegetables. Foods with increased processing tended to have reduced PyC concentrations. This survey of commonly consumed plant foods in the United States demonstrates PyCs are widely distributed and provides a foundation for understanding their concentrations and impact in the human diet.

Oxidative stress induced by cadmium in lettuce (Lactuca sativa Linn.): Oxidative stress indicators and prediction of their genes

Environmental contamination with heavy metals is of concern as plants have the ability to absorb chemical toxicants facilitating the entry of toxic metals into the food chain. Lettuce (Lactuca sativa Linn.) was cultured in four nutrient solutions containing different concentrations of cadmium (0, 3, 6, and 9 mmol). The impact of heavy metal on the morphological features, antioxidant properties and antioxidant enzymes activity were investigated with primary focus on superoxide dismutase, ascorbate peroxidase, peroxidase and catalase enzymes. In silico methods were utilized in the study of the genes of these enzymes. Significant changes were observed in the morphological features of the plant with plants appearing stunted, more spherical and yellow in colour. A decrease in the dry mass of the plant was also detected. The Translocation factor (TF) for cadmium was significantly high in lettuce. Enhanced antioxidant enzymatic activity suggests that these enzymes are integrally involved in the defense mechanism of the plant to heavy metal stress. Also observed was an increase in total soluble protein, and total phenolic content. Total flavonoid content was not significantly affected. Fourteen genes encoding for ascorbate peroxidase and nineteen genes for superoxide dismutase were identified in lettuce. These enzymes varied from each other with regards to the number of exons and amino acids present, as well as their location within the cell. Plants exhibit various response mechanisms to combat heavy metal contamination.

exposed to lead in hydroponics

Lead (Pb) is a major inorganic pollutant with no biological significance and has been a global concern. Phytotoxicity of lead induces toxic effects by generating reactive oxygen species (ROS), which inhibits most of the cellular processes in plants. Hydro-ponic experiments were performed with Ricinus communis to investigate the toxicity and antioxidant responses by exposing to different concentrations of lead (0, 200 and 400 µM) for 10 days. Pb stress caused a significant increase in electrolyte leakage, non-enzymatic antioxidants (phenols and flavonoids) and a decrease in the elemental profile of the plant. Histochemical visualization clearly indicates the significant increase of H2O2 production in dose-dependent manner under Pb stress. Likewise, an increase in catalase, guaiacol peroxidase and superoxide dismutase activity was also evident. Ascorbate peroxidase and MDAR, on the other hand, responded biphasically to Pb treatments showing a decrease in concentration. The decline in redox ratio GSH/GSSG was imposed by the indirect oxidative stress of Pb. Hence these findings showed the ameliorative potential of R. communis to sustain Pb toxicity under oxidative stress.